Method for reversing a vehicle combination

ABSTRACT

The disclosure relates to a method for reversing a vehicle combination (1) comprising a towing vehicle (10) and at least one trailer (20), said method comprising: (S10) reversing the vehicle combination, (S20) determining whether a jack-knifing condition (J) is about to occur by comparing a predicted future estimate of the articulation angle (Φ) with a maximum safe articulation angle (Φlim), wherein the maximum safe articulation angle (Φlim) is estimated according to the first aspect of the invention, and when it is determined that the jack-knifing condition (J) is about to occur, perform at least one of the following steps: (S30) issue a warning signal, and (S40) initiate a braking action for the vehicle combination, wherein the predicted future estimate of the articulation angle (Φ) is based on an estimated driver reaction time for initiating a braking action.

TECHNICAL FIELD

The invention relates to a method for estimating a maximum safearticulation angle to be used in reversing of a vehicle combinationcomprising a towing vehicle and at least one trailer. Moreover, theinvention relates to a method for reversing a vehicle combinationcomprising a towing vehicle and at least one trailer.

The invention can be applied in heavy-duty vehicles, such as trucks,buses and construction equipment. Although the invention will bedescribed with respect to a truck, the invention is not restricted tothis particular vehicle, but may also be used for any kind of towingvehicles connectable to a trailer.

BACKGROUND

Reversing of a vehicle combination, e.g. a trailer connected to a towingvehicle, is by many recognized as a challenging task. When a driver isreversing such a vehicle combination, the reversing speed usually has tobe lower compared to if no trailer is connected to the vehicle.

One issue that should be avoided during a reversing operation is toreach a so called jack-knifing condition. Jack-knifing is a well-knownissue for vehicle combinations, and may be defined as the folding of thevehicle combination between two connected members, e.g. truck/trailer ortrailer/trailer, so that it resembles the acute angle of a foldingpocket knife. In other words, a jack-knifing condition may be regardedas the condition when two connected members of the vehicle combinationhave reached an articulation angle such that the two members hit/crashinto each other.

On the other hand, in order to be able to reverse a vehicle combinationin an efficient manner, it may also be important to avoid a too largesafety margin before reaching the jack-knifing condition.

US patent application no. 2015/066296 A1 discloses a traileridentification system for trailer backup assist. The system communicatespredetermined trailer parameters, which are embedded on a tag attachedto the trailer, to a controller in the trailer backup assist system. Atrailer backup assist system is configured using the predeterminedtrailer parameters and the configured trailer backup assist system isactivated to operate using the trailer parameters.

SUMMARY

An object of the invention is to provide an improved method forestimating a maximum safe articulation angle to be used in reversing ofa vehicle combination. Another object of the invention is to provide animproved method for reversing a vehicle combination comprising a towingvehicle and at least one trailer.

According to a first aspect of the invention, the objects are achievedby a method for estimating a maximum safe articulation angle asdisclosed herein. According to a second aspect of the invention, theobjects are achieved by a method according to claim 1. According to athird aspect of the invention, the objects are achieved by a controlunit according to claim 12. According to a fourth aspect of theinvention, the objects are achieved by a towing vehicle according toclaim 13. According to a fifth aspect of the invention, the objects areachieved by a computer program according to claim 16. According to asixth aspect of the invention, the objects are achieved by computerreadable medium carrying a computer program according to claim 17.

According to the first aspect thereof, the objects are achieved by amethod for estimating a maximum safe articulation angle to be used inreversing of a vehicle combination comprising a towing vehicle and atleast one trailer, the method comprising:

-   -   receiving a preset maximum safe articulation angle for the        towing vehicle or the vehicle combination,    -   receiving a signal being indicative of an articulation angle of        the vehicle combination during forward driving of the vehicle        combination, and    -   updating the maximum safe articulation angle when the        articulation angle of the vehicle combination during forward        driving is larger than the preset maximum safe articulation        angle.

By the provision of the aforementioned method, an improved method ofobtaining a maximum safe articulation angle to be used during reversingof a vehicle combination is obtained. More particularly, updating themaximum safe articulation angle when it is recognized that a largerangle is used during forward driving provides an increased flexibilityduring a reversing operation. Towing vehicles' and trailers' dimensionsare generally not standardized. This is for example the case forheavy-duty towing trucks and trailers, where the towing truck duringoperation is usually switching between towing different types oftrailers. The trailers may have very different dimensions andproportions, which also may not be known beforehand. In addition, atrailer's dimensions and proportions may also change over time. Forexample, a trailer loaded with a bulky cargo extending outside the outerperimeter of the trailer will increase the width of the trailer.Correspondingly, a trailer width may be decreased when a bulky cargo isremoved therefrom. Therefore, the maximum safe articulation angle to beused during reversing may be very different depending on the type oftrailer connected to the towing vehicle. By the provision of theaforementioned method, an improved estimation of the maximum safearticulation angle can be performed due to that the articulation angleduring forward driving is recorded and used for updating the maximumsafe articulation angle. Additionally, an advantage of the presentinvention is that it provides a simple and efficient way of updating themaximum safe articulation angle without a need of knowing thedimensions/proportions of the vehicle combination. Instead, only theprovided articulation angle during forward driving may be required forupdating the maximum safe articulation angle.

The maximum safe articulation angle may be defined as an articulationangle which should not be exceeded in order to avoid a jack-knifingcondition. Thus, this angle may be used as a limit during a reversingoperation to thereby avoid the jack-knifing condition. An articulationangle is commonly the articulation angle between the towing vehicle andthe trailer, but it may also be an articulation angle between twoconnected trailers. Hence, the vehicle combination may also be a seriesof connected vehicles and comprise at least one towing vehicle and aplurality of trailers connected thereto.

Moreover, at least in the case of manual driving it is in general easierfor a driver to avoid running into a jack-knifing situation when drivingforwards than what it is when reversing. This is because, in forwarddriving, an articulated vehicle combination will straighten out if thesteering wheel angle is reduced. In reverse driving this is in generalnot the case. This difference is utilized by the present invention, inthe respect that a driver's ability in conveying a vehicle combinationsafely in forward direction is translated so that also reversing can bemade safer.

A preset maximum safe articulation angle may be an angle which is presetfor the specific towing vehicle and/or vehicle combination. The presetangle may also be entered manually by e.g. an operator of the towingvehicle or obtained from a database.

The signal received which is indicative of the articulation angle of thevehicle combination during forward driving of the vehicle combinationmay be obtained by different means. For example, the signal may beprovided by an angle sensor that measures the articulation angle betweentwo connected vehicles, e.g. truck/trailer. Alternatively, orcomplementary, the signal indicative of the articulation angle maycomprise information from a camera estimating a distance to theconnected vehicle, a distance sensor, a position signal from e.g. a GPS(Global Positioning System) on the connected vehicle, or any other meansthat can provide the articulation angle.

Optionally, the signal being indicative of the articulation angle may becontinuously or intermittently recorded during forward driving. Forexample, if the signal is intermittently recorded, the articulationangle during forward driving may not need to be recorded until thearticulation angle reaches a certain threshold value, which value may beclose to the preset maximum safe articulation angle, such as 30, 20 or10 degrees from the preset maximum safe articulation angle.Alternatively, or complementary, the articulation angle during forwarddriving may only be recorded at certain speeds of the vehiclecombination, at certain time intervals etc. In the latter example, anoperator of the vehicle combination may for example select when thearticulation angle should be recorded, such as when the operatorrecognizes that a large articulation angle is used during forwarddriving of the vehicle combination.

Optionally, the method may further comprise the additional step of:

-   -   updating the maximum safe articulation angle when it has been        determined that a jack-knifing condition has occurred, whereby        the updated maximum safe articulation angle corresponds to an        articulation angle which occurred prior to the determined        jack-knifing condition. This updating of the maximum safe        articulation angle may be determined in any one of a forward        driving or reversing situation of the vehicle combination.

Hence, if it is determined that a jack-knifing condition has occurred,the maximum safe articulation angle may be updated, thereby providing amaximum safe articulation angle which better corresponds to the truejack-knifing angle of the vehicle combination. An angle occurring priorto the determined jack-knifing condition may be an angle which is offsetby certain degrees from the jack-knifing angle, such as 10, 9, 8, 7, 6,5, 4, 3, 2, 1 degree(s) or less from the determined jack-knifing angle.Alternatively, or complementary, the angle occurring prior to thedetermined jack-knifing condition may be an angle which is recorded acertain time period prior to the jack-knifing condition occurred, suchas 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 second(s) or less prior to when thedetermined jack-knifing condition occurred.

Still optionally, the jack-knifing condition may be determined byreceiving a signal that indicates that at least one of the followingevents has occurred:

-   -   an emergency call from the vehicle combination has been issued,    -   an airbag of the towing vehicle has been deployed,    -   a yaw, pitch or roll rate for the towing vehicle or the at least        one trailer has exceeded a preset threshold value,    -   a longitudinal or lateral acceleration for the towing vehicle or        the at least one trailer has exceeded a preset threshold value,    -   a force in a trailer coupling has exceeded a preset threshold        value,    -   a speed reduction of the towing vehicle or the vehicle        combination has exceeded a preset threshold value,    -   a value being indicative of a second time derivative of the        articulation angle has exceeded a preset threshold value.

Hence, by using a signal that indicates any one of the above mentionedevents, an improved identification of a jack-knifing condition may beobtained, which in turn may provide an improved value for the updatedmaximum safe articulation angle.

Optionally, the updated maximum safe articulation angle may also beshared with other vehicles. For example, if it is determined that aspecific type of towing vehicle and trailer combination can have alarger maximum safe articulation angle, that information may be sharedto other towing vehicles which are of similar type. Purely by way ofexample, the information may be shared by wireless transmission, e.g.5g, 4g, 3g, Bluetooth, WiFi communication. The updated information mayalso be stored in a database, placed in the vehicle and/or in a remotedatabase.

According to the second aspect thereof, the objects are achieved by amethod for reversing a vehicle combination comprising a towing vehicleand at least one trailer, the method comprising:

-   -   reversing the vehicle combination,    -   determining whether a jack-knifing condition is about to occur        by comparing a predicted future estimate of the articulation        angle with the maximum safe articulation angle as estimated        according to any one of the embodiments of the first aspect of        the invention, and when it is determined that the jack-knifing        condition is about to occur, perform at least one of the        following steps:    -   issue a warning signal, and    -   initiate a braking action for the vehicle combination,

wherein the predicted future estimate of the articulation angle is basedon an estimated driver reaction time for initiating a braking action.

By the provision of the aforementioned method, an improved reversingoperation may be obtained, which is safe and provides increasedflexibility by using the updated maximum safe articulation angle. Hence,larger articulation angles may therefore be used during reversing.Additionally, by issuing a warning signal and/or initiate a brakingaction if it is determined that the jack-knifing condition is about tooccur, a safer reversing may be obtained. It shall be noted that allembodiments of the first aspect of the invention are applicable to allof the embodiments of the second aspect of the invention, and viceversa. The predicted future estimate of the articulation is an estimateof the articulation angle which the vehicle combination will have at alater point in time during the reversing operation. Hence, during areversing operation, it is possible to estimate the evolvement of thearticulation angle. The braking action may be initiated by for example adriver assistance system of the towing vehicle, and by considering thedriver reaction time for initiating a braking action, the estimation canbe improved. The warning signal may be any kind of warning signal, suchas a warning signal to a driver of the vehicle being in the form of avisual warning, acoustic warning, tactile warning or any combinationthereof. The warning signal may also be any kind of warning signal to aremote operator/user of the vehicle combination, e.g. if the towingvehicle is an autonomous vehicle or remotely controlled.

Optionally, the predicted future estimate is based on the estimateddriver reaction time from the warning signal is issued until a brakingaction has been initiated by the driver.

Optionally, the predicted future estimate of the articulation angle maybe derived from the current articulation angle and a first order timederivative of the current articulation angle. The current articulationangle is the articulation angle which the vehicle combination currentlyhas during the reversing operation. The first order time derivative ofthe current articulation angle may also be derived from a first ordervehicle travel distance derivative of the articulation angle and areversing speed of the vehicle. Still optionally, the predicted futureestimate of the articulation angle may be derived from the currentarticulation angle and a second order time derivative of the currentarticulation angle. Similarly, the second order time derivative of thecurrent articulation angle may also be derived from a second ordervehicle travel distance derivative of the articulation angle and areversing speed of the vehicle.

Optionally, the braking action may be initiated when the followingcondition is fulfilled:

${{\varphi + \frac{\overset{.}{\varphi}\; v_{x}}{a_{x}} + {{\overset{¨}{\varphi}\left( \frac{v_{x}}{a_{x}} \right)}^{2}/2}}} > \varphi_{{li}\; m}$

wherein v_(x) corresponds to a reversing speed, a_(x) corresponds to anachievable acceleration rate of the vehicle combination's brakingsystem, ϕ corresponds to the articulation angle, {dot over (ϕ)}corresponds to the first order time derivative of the articulationangle, {umlaut over (ϕ)} corresponds to the second order time derivativeof the articulation angle and ϕ_(lim) corresponds to the maximum safearticulation angle. The first and second order time derivatives may herealso be replaced by the first and second order vehicle travel distancederivatives of the articulation angle and a reversing speed of thevehicle.

Optionally, the warning signal may be issued when the followingcondition is fulfilled:

${{\varphi + {\overset{.}{\varphi}\left( {\frac{v_{x}}{a_{x}} + t_{reac}} \right)} + {{\overset{¨}{\varphi}\left( {\frac{v_{x}}{a_{x}} + t_{reac}} \right)}^{2}/2}}} > \varphi_{{li}\; m}$

wherein v_(x) corresponds to the reversing speed, a_(x) corresponds tothe achievable acceleration rate of the vehicle combination's brakingsystem, ϕ corresponds to the articulation angle, {dot over (ϕ)}corresponds to the first order time derivative of the articulationangle, {umlaut over (ϕ)} corresponds to the second order time derivativeof the articulation angle (ϕ), t_(reac) corresponds to an estimateddriver reaction time from the warning signal is issued until a brakingaction has been initiated by the driver and ϕ_(lim) corresponds to themaximum safe articulation angle. The first and second order timederivatives may here also be replaced by the first and second ordervehicle travel distance derivatives of the articulation angle and areversing speed of the vehicle. The estimated driver reaction time maybe differently set depending on the driver. Examples of driver reactiontimes are 1 second or tenths of a second, such as 0.1, 0.2, 0.3, 0.4seconds or more. Still optionally, a fraction of an estimated driverreaction time may also be used, such as 70, 80 or 90% of the estimateddriver reaction time.

Optionally, a value being indicative of a current steering wheel angleor a first time derivative of the steering wheel angle may also used fordetermining if a jack-knifing condition is about to occur. This mayfurther improve the estimation of the predicted future estimate of thearticulation angle. The steering wheel angle and the derivative of thesteering wheel angle may correlate to the articulation angle and thederivative of the articulation angle and may therefore be used forestimating a predicted future estimate of the articulation angle.Particularly suited for the operation may be a vehicle model, forinstance a linear bicycle model, including one or several trailersdeveloped for reversing. Another alternative may be a kinematic bicyclemodel. Both models are known for the skilled person, and will thereforenot be described in more detail herein.

Optionally, at least one of a steering operation and a speed controloperation of the vehicle combination during reversing may be performedautomatically without any direct human involvement. Thus, the reversingoperation may be semi-automatic or even fully automatic. For example,the driver may only instruct the towing vehicle to start a reversingoperation to a certain destination, such as a loading/unloading dockingstation, and thereafter let the towing vehicle automatically reversewith the trailer(s) until it reaches its destination. Hence, by theprovision of the invention, the reversing operation may be performed athigher speeds without compromising with safety.

Optionally, the warning signal may comprise different levels/amplitudesdepending on how close to the jack-knifing condition the vehiclecombination comes. Hence, it may also be estimated how long time it willtake until the vehicle combination reaches a jack-knifing condition ifcontinuing the reversing operation.

Optionally, the initiated braking action may be interrupted or evendeactivated by e.g. a driver of the towing vehicle when pressing on anacceleration pedal in the towing vehicle. There may be situations whenthe driver may “override” the intention of the method, such as if thedriver wants to reach a jack-knifing condition.

According to the third aspect thereof, the objects are achieved by acontrol unit for controlling a towing vehicle, wherein the control unitis configured to perform the steps of the method according to any one ofthe embodiments of the first aspect of the invention and/or the steps ofthe method according to any one of the embodiments of the second aspectof the invention. Hence, the methods as disclosed herein mayadvantageously be integrated into a control unit. The control unit maypreferably be integrated into the towing vehicle. The advantages of thecontrol unit are largely analogous to the advantages provided by themethods as disclosed herein, and will therefore not be furtherelaborated here. In addition, all aspects of the third aspect of theinvention are applicable to all aspects of the first and second aspectsof the invention, and vice versa.

According to the fourth aspect thereof, the objects are achieved by atowing vehicle comprising a control unit according to any one of theembodiments of the third aspect of the invention. The advantages of thetowing vehicle are largely analogous to the advantages provided by thecontrol unit and the methods as disclosed herein, and will therefore notbe further elaborated here. In addition, all aspects of the fourthaspect of the invention are applicable to all aspects of the first,second and third aspects of the invention, and vice versa.

Optionally, the towing vehicle may be a semi-autonomous or a fullyautonomous vehicle.

As already indicated hereinabove, the towing vehicle may be connected toat least one trailer, whereby an articulation angle may be any one ofthe articulation angles between two interconnected vehicles, i.e. towingvehicle/trailer and trailer/trailer. Still further, even though theinvention is mainly described in relation to towing trucks, it maylikewise be used for other types of towing vehicles, such as passengervehicles, i.e. passenger cars, construction equipment vehicles, busesetc.

Optionally, the towing vehicle may comprise means for measuring and/orestimating an articulation angle between the towing vehicle and aconnected trailer and/or between two interconnected trailers. As alreadymentioned hereinabove, the means for measuring and/or estimating thearticulation angle may be an angle sensor that measures the articulationangle between two connected vehicles, e.g. truck/trailer. Alternatively,or complementary, the signal indicative of the articulation angle maycomprise information from a camera estimating a distance to theconnected vehicle, a distance sensor, a position signal from e.g. a GPS(Global Positioning System) on the connected vehicle, or any other meansthat can provide a measurement or estimation of the articulation angle.

According to the fifth aspect thereof, the objects are achieved by acomputer program comprising program code means for performing the stepsof any one of the embodiments of the methods of the first and secondaspect of the invention when said program is run on a computer.

According to the sixth aspect thereof, the objects are achieved by acomputer readable medium carrying a computer program comprising programcode means for performing the steps of any one of the embodiments of themethods of the first and second aspect of the invention when saidprogram product is run on a computer.

Further advantages and advantageous features of the invention aredisclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detaileddescription of embodiments of the invention cited as examples.

In the drawings:

FIG. 1 is showing a schematic illustration of a vehicle combinationaccording to an example embodiment of the present invention,

FIG. 2 is showing another schematic illustration of a vehiclecombination according to an example embodiment of the present invention,

FIG. 3 is showing another schematic illustration of a vehiclecombination performing a reversing operation according to an exampleembodiment of the present invention,

FIG. 4 is showing a principle illustration of a vehicle combination withan articulation angle according to an example embodiment of the presentinvention

FIG. 5 is showing another principle illustration of a vehiclecombination with a maximum safe articulation angle according to anexample embodiment of the present invention,

FIG. 6 shows a flowchart of a method according to an example embodimentof the first aspect of the invention, and

FIG. 7 shows a flowchart of a method according to an example embodimentof the second aspect of the invention.

The drawings show diagrammatic exemplifying embodiments of the presentinvention and are thus not necessarily drawn to scale. It shall beunderstood that the embodiments shown and described are exemplifying andthat the invention is not limited to these embodiments. It shall also benoted that some details in the drawings may be exaggerated in order tobetter describe and illustrate the invention. Like reference charactersrefer to like elements throughout the description, unless expressedotherwise.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

In FIG. 1, a schematic illustration of a vehicle combination 1, seenfrom above, according to an example embodiment of the present inventionis depicted. The vehicle combination 1 comprises a towing vehicle 10, inthis embodiment a towing truck, and a trailer 20 connected to the towingtruck 10 via a coupling 21. The towing vehicle 10 and the trailer arepivotably movable around the coupling 21, whereby an articulation angleϕ of the vehicle combination 1 is the relative angle between the towingvehicle 10 and the trailer in respect of the coupling 21. For moredetails about the articulation angle ϕ, see e.g. FIGS. 4 and 5. FIG. 1illustrates when the vehicle combination 1 has reached a jack-knifingcondition J, i.e. the towing vehicle 10 and the trailer 20 have reachedsuch a large articulation angle ϕ that the two vehicles, truck/trailer,have hit into each other at the point J. In one example embodiment, acabin of the truck 10 may have hit a side of the trailer 20. During areversing operation of the vehicle combination 1, it may be important toavoid reaching the jack-knifing condition J. Thereby it may be requiredto provide a preset maximum safe articulation angle during the reversingoperation. The preset angle may for example be provided to the driver,e.g. via a display, such that the driver during reversing checks thatthe maximum safe articulation angle is not reached by comparing saidangle to the current articulation angle (I). Alternatively, orcomplementary, a driver assistance system may use the maximum safearticulation angle as input during the reversing operation forcontrolling the reversing operation. Hence, the driver assistance systemmay control the reversing operation such that the articulation angle ϕwill not exceed the maximum safe articulation angle ϕ_(lim). By theprovision of the present invention, a more efficient reversing operationmay be accomplished. More particularly, by receiving a signal beingindicative of the articulation angle ϕ during forward driving of thevehicle combination 1, and updating the preset maximum safe articulationangle ϕ_(lim) when the articulation angle ϕ of the vehicle combination 1during forward driving is larger than the preset maximum safearticulation angle ϕ_(lim), an even larger range of articulation anglesϕ may be allowed during a subsequent reversing operation withoutreaching the jack-knifing condition J.

In FIG. 2, another schematic illustration of a vehicle combination 1 isdepicted, showing another example of a jack-knifing condition J. Here,the towing truck 10 has hit into a trailer supporting leg 22 of thetrailer 20.

In FIG. 3, a schematic illustration of a vehicle combination 1 during areversing operation can be seen. The towing truck 10 is reversing at aspeed v_(x) and is connected via a coupling 21 to a trailer 20. Thereversing speed v_(x) is this in this embodiment the speed of the towingtruck 10, but may also be regarded as a translation speed of thearticulation point 21, i.e. the coupling 21. Moreover, the towing truckmay also brake, resulting in a braking acceleration a_(x), i.e. adeceleration, in an opposite direction to the truck speed v_(x). Duringthe reversing operation, the vehicle combination 1 may advantageouslymake use of the updated maximum safe articulation angle ϕ_(lim) in orderto avoid a jack-knifing condition J and also to be able to in anefficient manner complete the reversing operation.

A control unit 11 may be integrated in the towing truck 1, and beingconfigured to perform the steps of the methods according to any one ofthe embodiments of the first and/or second aspects of the presentinvention. As already indicated hereinabove, the reversing operation maybe performed semi-automatically or even fully automatically by e.g. thecontrol unit 11 controlling any one of a steering operation and avehicle speed v_(x). Alternatively, the reversing operation may also beperformed manually by a driver of the vehicle 10.

In FIGS. 4 and 5, the articulation angle ϕ and the maximum safearticulation angle ϕ_(lim) of a vehicle combination 1 can be moreclearly seen. The figures depict principle illustrations of a vehiclecombination 1 which are connected and pivotably movable around thecoupling 21, i.e. the articulation point. FIG. 4 may be regarded as asituation during reversing, such as can be seen in FIG. 3, where thevehicle combination 1 in a particular point in time during the reversingoperation has a current articulation angle ϕ which is smaller than themaximum safe articulation angle ϕ_(lim) as e.g. seen in FIG. 5. Thus,during the reversing operation as shown in FIG. 4, the articulationangle ϕ should not exceed the maximum safe articulation angle ϕ_(lim),and by the provision of the present invention, a larger range ofarticulation angles ϕ may be allowed during the reversing operationwithout reaching a jack-knifing condition J.

The illustration in FIG. 5 may for example represent a situation duringforward driving of the vehicle combination 1 where the maximum safearticulation angle ϕ_(lim) is larger than a preset maximum safearticulation angle. Hence, a control unit 11 of the towing vehicle 1 maythereafter update the preset maximum safe articulation to the new andlarger maximum safe articulation angle ϕ_(lim). The expression “duringforward driving” as used herein means thus that the vehicle combination1 or the towing vehicle 10 is having a speed v_(x) which is larger thanzero and in a forward direction in respect of the vehicle combination 1or the towing vehicle 10. Hence, the vehicle combination 1 may beregarded as being in use or in operation.

FIGS. 6 and 7 show flowcharts of example embodiments of the respectivemethods according to the first and second aspects of the invention.

In step S1 in FIG. 6, a preset maximum safe articulation angle ϕ_(lim)is provided for the towing vehicle 10 or the vehicle combination 1.Purely by way of example, the preset maximum safe articulation angleϕ_(lim) may be set to 100 degrees. In step S2, a signal is receivedbeing indicative of the articulation angle ϕ of the vehicle combination1 during forward driving of the vehicle combination 1. For example, thevehicle combination 1 may be in use and driving forwardly at a shippingterminal area/logistics center area where it is required to make turnswith large articulation angles ϕ. Hence, when it is recognized that thearticulation angle ϕ is larger than the preset maximum safe articulationangle ϕ_(lim) during the forward driving, the maximum safe articulationangle ϕ_(lim) may be updated in step S3. Purely by way of example, itmay be recognized that the articulation angle ϕ during forward drivingis 105 degrees, i.e. larger than the preset maximum safe articulationangle of 100 degrees as mentioned hereinabove. Thereafter, a largermaximum safe articulation angle ϕ_(lim), i.e. 105 degrees, may be usedas a limit during a subsequent reversing operation of the vehiclecombination 1. As a complement, the maximum safe articulation angleϕ_(lim) may also be updated in step S4 when it has been determined thata jack-knifing condition J has occurred, whereby the updated maximumsafe articulation angle ϕ_(lim) corresponds to an articualation angle ϕwhich occurred prior to the determined jack-knifing condition J. Purelyby way of example, in relation to the aforementioned example, it may bedetermined that a jack-knifing condition occurs already at 98 degreesarticulation angle ϕ, i.e. a value which is smaller than the presetmaximum safe articulation angle of 100 degrees. Thereby, the maximumsafe articulation angle ϕ_(lim) may be updated to an angle being lessthan 98 degrees instead of 100 degrees, such as 97 degrees or less. Thejack-knifing condition J may occur both at forward and rearward driving,and as already explained hereinabove, the jack-knifing condition may bedetermined by receiving a signal, to e.g. the control unit 11, thatindicates that at least one of the following events has occurred:

-   -   an emergency call from the vehicle combination has been issued,    -   an airbag of the towing vehicle has been deployed,    -   a yaw, pitch or roll rate for the towing vehicle or the at least        one trailer has exceeded a preset threshold value,    -   a longitudinal or lateral acceleration for the towing vehicle or        the at least one trailer has exceeded a preset threshold value,    -   a force in a trailer coupling has exceeded a preset threshold        value,    -   a speed reduction of the towing vehicle or the vehicle        combination has exceeded a preset threshold value,    -   a value being indicative of a second time derivative of the        articulation angle has exceeded a preset threshold value.

Vehicles may have integrated solutions for contacting emergencyassistance (SOS). An emergency call (or message) can either be triggeredby a button accessible to a driver of the vehicle 10 or automaticallyafter e.g. air-bag deployment. The occurrence of an emergency call (ormessage) can be used as an indication of a possible jack-knifingcondition J. It can thus be used to trigger a reset of ϕ_(lim) to thevalue held prior to the event.

Vehicles may also have collision detection sensors installed in variousparts of the vehicle. The primary purpose is normally to trigger air-bagafter collision. A collision with an obstacle can either be aconsequence of a jack-knifing condition J or a jack-knifing condition Jcould occur after a collision. Irrespective of the case, the onset of acollision sensor could be used to reset ϕ_(lim) to the value held priorto the event.

A gyroscope may be used to measure either yaw, pitch or roll ratedepending on its physical orientation on the vehicle 10. If either ofthese signals is observed to have a substantially larger absolute valuethan what is normal during normal driving it can indicate that ajack-knifing condition J has occurred. It can thus be used to trigger areset of ϕ_(lim) to the value held prior to the event. Abnormality maybe defined with a preset limit value.

An accelerometer may be used to measure either longitudinal or lateralacceleration depending on its physical orientation on the vehicle 10. Ifeither of these signals is observed to have a substantially largerabsolute value than what is normal during normal driving it can indicatethat a jack-knifing condition J has occurred. It can thus be used totrigger a reset of ϕ_(lim) to the value held prior to the event.Abnormality may be defined with a preset limit value.

A strain gage, or other devices, may be used to measure forces indifferent directions in the trailer coupling 21. If either of thesesignals is observed to have a substantially larger absolute value thanwhat is normal during normal driving it can indicate that a jack-knifingcondition J has occurred. It may thus be used to trigger a reset ofϕ_(lim) to the value held prior to the event. Abnormality may be definedwith a preset limit value.

Wheel speed sensors, GPS, Lidars, crank-shaft speed sensors etc. are alldifferent devices that may be used to measure vehicle speed v_(x). Anabnormal discontinuity in any of these speed measurements may be used toreset ϕ_(lim) to the value held prior to the event. More in detail,discontinuity may be defined as a certain, preset, change in signalvalue within a set time interval.

Trailer-mounted mechanical rotational angle sensors, GPS, Lidars,truck-mounted mechanical rotational angle sensors etc. are all differentdevices that may be used to measure the articulation angle (I). Anabnormal discontinuity in any of these measurements may be used to resetϕ_(lim) to the value held prior to the event. More in detail,discontinuity may be defined as a certain, preset, magnitude in signalsecond derivative.

The flowchart in FIG. 7 shows a method of reversing a vehiclecombination 1 comprising a towing vehicle 1 and at least one trailer 20,whereby a reversing operation is initiated in step S10. As alreadymentioned hereinabove, the reversing operation may be manual,semi-automatic or even fully automatic, and controlled by the controlunit 11 in the towing vehicle 10. In a following step S20, the controlunit 11 may determine whether a jack-knifing condition J is about tooccur by comparing a predicted future estimate of the articulation angleϕ with the maximum safe articulation angle ϕ_(lim) as estimatedaccording to the first aspect of the present invention, such as shownand described in respect of FIG. 6. When it is determined that thejack-knifing condition is about to occur, at least one of a warningsignal may be issued, represented by step S30, and a braking action maybe initiated for the vehicle combination 1, represented by step S40,wherein the predicted future estimate of the articulation angle ϕ isbased on an estimated driver reaction time for initiating a brakingaction.

It is to be understood that the present invention is not limited to theembodiments described above and illustrated in the drawings; rather, theskilled person will recognize that many changes and modifications may bemade within the scope of the appended claims.

1. A method for reversing a vehicle combination comprising a towingvehicle and at least one trailer, the method comprising: reversing, by acontrol unit, the vehicle combination; and determining, by the controlunit, whether a jack-knifing condition is about to occur by comparing apredicted future estimate of the articulation angle with a maximum safearticulation angle, wherein the predicted future estimate of thearticulation angle is based on an estimated driver reaction time forinitiating a braking action, wherein the maximum safe articulation angleis estimated by: receiving, by the control unit, a preset maximum safearticulation angle for the towing vehicle or the vehicle combination;receiving, by the control unit, a signal indicative of an articulationangle of the vehicle combination during forward driving of the vehiclecombination; and updating, by the control unit, the maximum safearticulation angle when the articulation angle of the vehiclecombination during forward driving is larger than the preset maximumsafe articulation angle, and upon determination that the jack-knifingcondition is about to occur, performing at least one of: issue, by thecontrol unit, a warning signal; and initiate, by the control unit, abraking action for the vehicle combination.
 2. The method of claim 1,wherein the predicted future estimate is based on the estimated driverreaction time from the warning signal is issued until a braking actionhas been initiated by the driver.
 3. The method of claim 1, wherein thepredicted future estimate of the articulation angle is derived, by thecontrol unit, from the current articulation angle and a first order timederivative of the current articulation angle.
 4. The method of claim 1,wherein the predicted future estimate of the articulation angle isderived, by the control unit, from the current articulation angle and asecond order time derivative of the current articulation angle.
 5. Themethod of claim 1, wherein the braking action is initiated, by thecontrol unit, when the following condition is fulfilled:${{\varphi + \frac{\overset{.}{\varphi}\; v_{x}}{a_{x}} + {{\overset{¨}{\varphi}\left( \frac{v_{x}}{a_{x}} \right)}^{2}/2}}} > \varphi_{{li}\; m}$wherein v_(x) corresponds to a reversing speed, a_(x) corresponds to anachievable acceleration rate of the vehicle combination's brakingsystem, ϕ corresponds to the articulation angle, {dot over (ϕ)}corresponds to the first order time derivative of the articulationangle, {umlaut over (ϕ)} corresponds to the second order time derivativeof the articulation angle and ϕ_(lim) corresponds to the maximum safearticulation angle.
 6. The method of claim 1, wherein the warning signalis issued, by the control unit, when the following condition isfulfilled:${{\varphi + {\overset{.}{\varphi}\left( {\frac{v_{x}}{a_{x}} + t_{reac}} \right)} + {{\overset{¨}{\varphi}\left( {\frac{v_{x}}{a_{x}} + t_{reac}} \right)}^{2}/2}}} > \varphi_{{li}\; m}$wherein v_(x) corresponds to the reversing speed, a_(x) corresponds tothe achievable acceleration rate of the vehicle combination's brakingsystem, ϕ corresponds to the articulation angle, {dot over (ϕ)}corresponds to the first order time derivative of the articulationangle, {umlaut over (ϕ)} corresponds to the second order time derivativeof the articulation angle, t_(reac) corresponds to an estimated driverreaction time from the warning signal is issued until a braking actionhas been initiated by the driver and ϕ_(lim) corresponds to the maximumsafe articulation angle.
 7. The method of claim 1, wherein a value beingindicative of a current steering wheel angle or a first derivative ofthe steering wheel angle is also used for determining, by the controlunit, if a jack-knifing condition is about to occur.
 8. The method ofclaim 1, wherein at least one of a steering operation and a speedcontrol operation of the vehicle combination during reversing isperformed automatically, by the control unit, without any direct humaninvolvement.
 9. The method of claim 1, wherein the signal beingindicative of the articulation angle is continuously or intermittentlyrecorded, by the control unit, during forward driving.
 10. The method ofclaim 1, further comprising updating, by the control unit, the maximumsafe articulation angle when it has been determined that a jack-knifingcondition has occurred, whereby the updated maximum safe articulationangle corresponds to an articulation angle which occurred prior to thedetermined jack-knifing condition.
 11. The method of claim 10, whereinthe jack-knifing condition is determined, by the control unit, byreceiving a signal that indicates that at least one of the followingevents has occurred: an emergency call from the vehicle combination hasbeen issued; an airbag of the towing vehicle has been deployed; a yaw,pitch or roll rate for the towing vehicle or the at least one trailerhas exceeded a preset threshold value; a longitudinal or lateralacceleration for the towing vehicle or the at least one trailer hasexceeded a preset threshold value; a force in a trailer coupling hasexceeded a preset threshold value; a speed reduction of the towingvehicle or the vehicle combination has exceeded a preset thresholdvalue; and a value being indicative of a second time derivative of thearticulation angle has exceeded a preset threshold value.
 12. A controlunit for controlling a towing vehicle, wherein the control unit isconfigured to: reverse a vehicle combination comprising the towingvehicle and at least one trailer; and determine whether a jack-knifingcondition is about to occur by comparing a predicted future estimate ofthe articulation angle with a maximum safe articulation angle, whereinthe predicted future estimate of the articulation angle is based on anestimated driver reaction time for initiating a braking action, whereinthe maximum safe articulation angle is estimated by: receiving a presetmaximum safe articulation angle for the towing vehicle or the vehiclecombination; receiving a signal being indicative of an articulationangle of the vehicle combination during forward driving of the vehiclecombination; and updating the maximum safe articulation angle when thearticulation angle of the vehicle combination during forward driving islarger than the preset maximum safe articulation angle, and upondetermination that the jack-knifing condition is about to occur, performat least one of: issue a warning signal; and initiate a braking actionfor the vehicle combination.
 13. A towing vehicle comprising a controlunit configured to: reverse a vehicle combination comprising the towingvehicle and at least one trailer; and determine whether a jack-knifingcondition is about to occur by comparing a predicted future estimate ofthe articulation angle with a maximum safe articulation angle, whereinthe predicted future estimate of the articulation angle is based on anestimated driver reaction time for initiating a braking action, whereinthe maximum safe articulation angle is estimated by: receiving a presetmaximum safe articulation angle for the towing vehicle or the vehiclecombination; receiving a signal being indicative of an articulationangle of the vehicle combination during forward driving of the vehiclecombination; and updating the maximum safe articulation angle when thearticulation angle of the vehicle combination during forward driving islarger than the preset maximum safe articulation angle, and upondetermination that the jack-knifing condition is about to occur, performat least one of: issue a warning signal; and initiate a braking actionfor the vehicle combination.
 14. The towing vehicle of claim 13, whereinthe vehicle is a semiautonomous or a fully autonomous vehicle.
 15. Thetowing vehicle according to claim 13, wherein the control unit isfurther configured to determine an articulation angle between at leastone of: the towing vehicle and a connected trailer; or between twointerconnected trailers. 16-17. (canceled)